1. Field of the Invention
This invention relates generally to cathode sputtering systems and more particularly to the attachment of a target to the cathode assembly of a sputtering system.
2. Description of the Prior Art
A cathode sputtering system is primarily used to deposit thin films of material upon substrates. Extensively used in the electronic industry, a sputtering system often includes an evacuable chamber, a cathode assembly and an anode assembly disposed within the chamber, and a target attached to the cathode assembly. The target is formed of the same material which is to be deposited upon the chosen substrate.
In use, a substrate is placed within the chamber, the chamber is partially evacuated and backfilled with an inert gas and a high voltage power supply is activated to develop a potential between the cathode and anode. The potential causes gas ions to accelerate toward the cathode assembly and to strike the target material with sufficient momentum to cause the target to partially vaporize. The vaporized target material diffuses throughout the chamber and deposits as an even coat upon the substrate.
In many modern cathode sputtering systems, permanent magnets are included within the structure of the cathode assembly so that lines of magnetic flux extend through the target material to form a "tunnel" shaped path along the surface of the target. The flux line tunnel substantially traps electrons, which interact with the gas to create the aforementioned ions. Thus, the ion density adjacent the target is greatly increased, resulting in high sputtering rates from the target.
In the prior art, targets were either brazed or soldered to the backing plate of the cathode assembly. Such attachments had the advantage of firmly retaining the target in position on the cathode assembly and further provided good thermal conduction from the target to the cathode assembly so that as the target became heated, the heat would be drawn from the target by the cathode assembly.
When a target is soldered or brazed to a cathode assembly, however, the problem of later removing the target is created. If, for instance, an operator wished to remove a worn out or defective target, or if the operator wished to replace the target with a target of different composition, a long and tedious target removal operation would be required. Furthermore, during the removal operation, the expensive targets are sometimes destroyed. Also, the time required for soldering or brazing a new target onto the backing plate is further inefficient and costly.